Not all ESXi releases, including patch updates are available as an ISO image that can be downloaded. Depending on the type of ESXi release, it will either be available as an ISO and Offline Bundle (zip) format which can downloaded from the ESXi Customer Connect portal or only as an Offline Bundle which must be downloaded from the VMware Patch portal.
I typically see folks forgetting about the VMware Patch portal, which also provides patch updates for the vCenter Server Appliance (VCSA), when they are searching for a new ESXi updates. Let's take a look at an example using the ESXi 7.0 Update 3 release, as you can see from the screenshot below, you can download 7.0 Update 3c, d, f and g from the Customer Connector portal but for 7.0 Update 3e, i, j and k you will need to use the VMware Patch portal.
As mentioned earlier, when downloading ESXi patches from the VMware Patch portal, they are only available in the Offline Bundle format, which might work for most typical patch use cases but in some scenarios, you may actually want it in an ISO format, especially for initial installation.
